Ultrafiltration, partitioning coefficient

Partition coefficients are usually determined using ultrafiltration" or NMR" or UV-vis ... 

Physicochemical parameters. Partition coefficients are the most common type of physicochemical parameter in a PBPK model. Values for these quantities can be measured through experimental means (e.g., equilibrating tissue homogenates in a vial with an atmosphere containing the test chemical [9,10], or from ultrafiltration/equilibrium dialysis studies for nonvolatile chemicals), or through the use of quantitative structure activity/property relationships (QSA(P)Rs) [11],... 

The principles of affinity chromatography can be combined with other operations of purification to improve them (Labrou and Clonis 1994). Affinity partition combines the selectivity of affinity ligation with aqueous two-phase extraction (Kamihira et al. 1992 Kohler et al. 1991) and has been successfully employed in enzyme recovery and purification (Johansson and Tjerneld 1989 Schustolla et al. 1992) obtaining impressive increases in the partition coefficient (Eq. 2.16) and therefore in yield of enzyme recovery (Eq. 2.17). Affinity partition has also been combined with membrane separation (affinity ultrafiltration), where a soluble... 

Knaak et al. (2008) reviewed the literature pertaining to in vitro methods for developing tissue blood partition coefficients for PBPK models. The experimental work of Jepson et al. (1992,1994) is significant. Ultrafiltration was used to develop tissue saline and tissue blood partition coefficients. No new studies of this nature were found during the preparation of this review on pyrethroids. Automated laboratory methods are still needed and must be developed to insure the partition coefficients obtained firom the use of mechanistic or QSAR models are reasonable (Payne and Kenny 2002 Rowland, personal communication). 

A micellar isolation method using an analytical ultracentrifuge and so avoiding the inherent errors associated with the use of membranes in the dialysis and ultrafiltration techniques, has been proposed by Park and Rippie [70]. In principle the solubilized systems are centrifuged under selected conditions such that about 40 % separation of micelles is achieved. By assuming that the apparent partition coefficient is independent of surfactant concentration, equations are presented whereby the distribution of the solubilizate can be calculated from analysis of the upper and lower portions of the contents of the centrifuge tube. 

We might feel that it should be easy to distinguish between the diffusion-based and the flow-based explanations for solvent permeability. In fact, it often is difficult to do so. The reason is that the partition coefficient or the diameter of any pores in a thin selective layer is difficult to measure. Even the membrane thickness is frequently not exactly known. As a result, there has been considerable controversy over which of these explanations is correct. For reverse osmosis, the consensus is strongly in favor of the diffusion-solubility mechanism of Eq. 18.3-15. For ultrafiltration, there is an overwhelming belief that the membrane does contain pores and hence should be described with Eq. 18.3-17,... 

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